Fuel - Effects of Derivative Instruments Gains and Losses (Details) (Cash Flow Hedging, USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013		Sep. 30, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Other Comprehensive Income (OCI) on Derivatives (Effective Portion)			$ 0		$ 7
Amount of Gain or (Loss) Recognized from AOCL into Income (Effective Portion)			0		25
Amount of Gain or (Loss) Recognized in Income on Derivatives (Ineffective Portion and Amount Excluded from Effectiveness Testing)			0	[1]	(3)	[1]
Fuel Contracts
Derivative Instruments, Gain (Loss) [Line Items]
Fuel derivative instrument gains or losses	0	0
Amount of Gain or (Loss) Recognized in Other Comprehensive Income (OCI) on Derivatives (Effective Portion)			0		7
Fuel Contracts | Fuel Expense
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized from AOCL into Income (Effective Portion)			0		25
Amount of Gain or (Loss) Recognized in Income on Derivatives (Ineffective Portion and Amount Excluded from Effectiveness Testing)			$ 0	[1]	$ (3)	[1]

[1] No portion of the loss was excluded from the assessment of hedge effectiveness for the periods then ended.